Do you start with a little riff, try to replicate the sound in your head, then build off that?
Do you start with a chord progression first?
Do you start with lyrics?
Do you improvise until you hear something you like?

I look forward to hearing your answers

__________________
"I think the most important thing about music is the sense of escape." - Thom Yorke

I'll start playing one song, and keep going for like a half hour on this one song. I'm really bad about not knowing when to stop.

But I'll play something for so long that eventually I'll start to realize, "Hey, I can add this chord or this lead line" and eventually I'll play a song for so long that it turns into a different song.